The present invention relates generally to medical devices and methods of use for the treatment and/or management of cardiovascular, neurological, and renal disorders, and more specifically to devices and methods for controlling the baroreflex system of a patient for the treatment and/or management of cardiovascular, neurological, and renal disorders and their underlying causes and conditions, more particularly to baroreflex systems and methods that allow a physician to program the device for providing a predetermined response to changes in the patient's condition.
Hypertension, or high blood pressure, is a major cardiovascular disorder that is estimated to affect 65 million people in the United States alone, and is a leading cause of heart failure and stroke. It is listed as a primary or contributing cause of death in over 200,000 patients per year in the United States alone. Hypertension occurs in part when the body's smaller blood vessels (arterioles) constrict, causing an increase in blood pressure. Because the blood vessels constrict, the heart must work harder to maintain blood flow at the higher pressures. Sustained hypertension may eventually result in damage to multiple body organs, including the kidneys, brain, eyes, and other tissues, causing a variety of maladies associated therewith. The elevated blood pressure may also damage the lining of the blood vessels, accelerating the process of atherosclerosis and increasing the likelihood that a blood clot may develop. This could lead to a heart attack and/or stroke.
Sustained high blood pressure may eventually result in an enlarged and damaged heart (hypertrophy), which may lead to heart failure. Heart failure is the final common expression of a variety of cardiovascular disorders, including ischemic heart disease. It is characterized by an inability of the heart to pump enough blood to meet the body's needs and results in fatigue, reduced exercise capacity and poor survival. Congestive heart failure (CHF) is an imbalance in pump function in which the heart fails to maintain the circulation of blood adequately. The most severe manifestation of CHF, pulmonary edema, develops when this imbalance causes an increase in lung fluid due to leakage from pulmonary capillaries into the lung. The most common cause of heart failure is coronary artery disease, which is secondary to loss of left ventricular muscle, ongoing ischemia, or decreased diastolic ventricular compliance. Other causes of CHF include hypertension, valvular heart disease, congenital heart disease, other cardiomyopathies, myocarditis, and infectious endocarditis.
One preferred heart failure treatment method is to use cardiac rhythm management devices (“cardiac rhythm management device”) such as cardiac resynchronization therapies (“CRT”) using pacemakers and combination pace makers/defibrillators (“ICD”). Another CHF treatment method that has been proposed is to affect the baroreflex system to help the heart perform more efficiently by way of controlling the patient's blood pressure. Baroreflex activation may generally decrease neurohormonal activation, thus decreasing cardiac afterload, heart rate, sympathetic drive to the heart and the like. By decreasing the demands placed on the heart, baroreflex activation may help prevent or treat CHF.
A number of different treatment modalities may be attempted for treating heart failure, such as medications, mechanical restriction of the heart, surgical procedures to reduce the size of an expanded heart and the like. These include vasodilators to reduce the blood pressure and ease the workload of the heart, diuretics to reduce fluid overload, inhibitors and blocking agents of the body's neurohormonal responses, and other medicaments. Various surgical procedures have also been proposed for these maladies. For example, heart transplantation has been proposed for patients who suffer from severe, refractory heart failure. Alternatively, an implantable medical device such as a ventricular assist device (VAD) may be implanted in the chest to increase the pumping action of the heart. Alternatively, an intra-aortic balloon pump (IABP) may be used for maintaining heart function for short periods of time, but typically no longer than one month.
Of course, no “perfect” treatment method for heart failure has yet been developed. Although some of the therapies mentioned above may be highly effective in some cases, some may have unwanted side effects or provide little benefit to some patients. Because CHF is such a pervasive health problem, with high morbidity, mortality and costs to society, improved treatment methods are continually sought. Additionally, with the use of any of such devices, the physiological conditions of a patient may change rapidly in response to internal and/or external conditions such that course of therapy may need to readjust to provide optimum performance to the patient.
Therefore, it would be desirable to provide improved methods and apparatus having smart processes for controlling their operation. Ideally, such methods and apparatus would be minimally invasive, with few if any significant side effects. Ideally, one or more underlying mechanisms causing heart failure could be treated in some cases. At least some of these objectives will be met by the present invention.